Mobile computing and/or communication devices are becoming smaller thereby driving the weight and size of data storage devices down. In a typical hard disk drive, the rotary voice coil actuator, including a voice coil, pivot bearing, E-block and suspensions, support the sliders with embedded read/write elements as they fly over the rotating disk in order to read information from and store information onto the disk medium. Thinner hard drive actuators can use a stainless steel arm to which a mount plate or suspension assembly is welded, creating a “unimount” arm/suspension assembly, instead of using an E-block.
As the number of tracks per inch (TPI) for drives increases, it is necessary to improve the accuracy of the servo-mechanical system that is following the servo information embedded on each track of the disk.
There are two common methods of improving track-following accuracy, using milliactuators and using microactuators, each in a two-stage servo-mechanical system. The “coarse” actuation arises from exciting the voice coil, rotating the entire actuator, while the “fine” actuation arises from moving either the complete loadbeam/slider assembly (milliactuator) or translating or rotating only the slider (micro actuator).
Milliactuators typically interpose a pair of piezoelectric actuators between the end of the arm and the loadbeam, such that expanding one piezoelectric actuator while contracting the other causes the loadbeam to rotate, displacing the slider at the end of the loadbeam. Because the inertia of the rotating portion of the loadbeam is smaller than the entire voice-coil actuator and has higher frequency resonances, it enhances the ability of the servo to follow more accurately.
Microactuators typically move or rotate only the slider or a portion of the slider. Since the slider is much less massive than the loadbeam, moving or rotating only the slider allows much better accuracy in following the tracks than does a milliactuator because fewer actuator and arm modes are excited. From a performance standpoint microactuators are preferred over milliactuators because they provide higher frequency resonance characteristics. However, microactuators involve very small, very precise parts that are more expensive to assemble and manufacture than the parts required for a milliactuator.
This leads to the need for a smaller milliactuator, one that uses less expensive components than microactuators and uses existing milliactuator manufacturing processes, but which can provide improved dynamics and hence improved servo-mechanical accuracy. Yet, as said before, with TPI for drives increasing, it is imperative to improve the accuracy of the servo-mechanical system that is following the servo information embedded on each track of the disk.
Thus, there is a need for apparati and methods for vibration compensation and suppression to improve the accuracy of track following in hard disk drives for both milliactuators and microactuators. Furthermore, other desirable features and characteristics will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and this background of the disclosure.